1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for providing a uniform cell gap in the liquid crystal display device.
2. Discussion of the Related Art
Generally, a liquid crystal display device has characteristics, such as low-voltage driving, low power consumption, full-color implementation, thin and compact size, and the like. Thus, it has been widely used for calculators, notebook computers, electronic watches, PC monitors, aircraft gauges, personal mobile terminals, mobile phones, etc.
Screens of liquid crystal display devices get wider and larger in size. In fabricating wide-screen liquid crystal display devices, a related art method for forming a liquid crystal layer by using vacuum injection takes too much time. Hence, a liquid crystal dropping method of dispensing liquid crystal droplets on a substrate under a vacuum condition has been widely used to resolve the problems in the conventional fabrication process.
When the liquid crystal layer is formed by the liquid crystal dropping method, a fabricating time can be reduced. The liquid crystal dropping method uses a UV-ray hardening sealant for bonding upper and lower substrates to each other.
The UV-ray hardening sealant is provided by mixing acrylate resin with a photo-hardener, which becomes a radical when a UV-ray is irradiated thereto at a predetermined ratio. The photo-hardener reacts with the acrylate to form polymer having strong adhesion to the glass substrate.
A spacer is used to maintain a uniform cell gap when the substrates are bonded to each other. The spacer types include a ball spacer scattered on the substrate and a column spacer formed on the substrate. The ball spacer may alter the cell gap when applied to a wide area. For this reason, the column spacer is mainly used.
When bonding the two substrates to each other by using a UV-ray hardening sealant, portions of the substrates with the sealant formed thereon are strongly bonded to each other. On the other hand, adhesion of the array portions of the substrates is weaker than that of the portions with the sealant. Thus, a stress is generated between the substrates.
A liquid crystal display device and a method of fabricating the same according to a related art are explained by referring to the attached drawings as follows.
FIG. 1 illustrates a layout of a liquid crystal display device by using a related art liquid crystal dropping method.
As shown in FIG. 1, a thin film transistor (TFT) array is formed in a liquid crystal display panel region on a first substrate 100. A silver (Ag) pattern for applying voltage to a terminal Vcom is formed on the periphery of the liquid crystal display panel region. Liquid crystal droplets are then dispensed onto the liquid crystal display panel region. The liquid crystal display panel region has an active area 120 and a dummy area 130.
Meanwhile, a color filter pattern is formed in the liquid crystal display panel region on a second substrate 150. Column spacers 105 are formed in the active area 120 to correspond to a wiring part excluding a pixel region 112 of the first substrate 100. The column spacers 105 formed on the second substrate 150 are then attached to the second substrate 150. After forming the column spacers 105, a UV-ray hardening sealant pattern 110 is formed on the periphery of the liquid crystal display panel region on the second substrate 150.
Subsequently, a liquid crystal display panel is prepared by bonding the first and second substrates 100 and 150 to each other. A UV-ray is then applied to the UV-ray hardening sealant 110 to harden the UV-ray hardening sealant 110.
The column spacers 105 maintain a uniform cell gap in the active area 120 on the entire surface of the liquid crystal display device. Meanwhile, due to its strong adhesion, the UV-ray hardening sealant pattern 110 pulls the first and second substrates 100 and 150. Therefore, a portion where the sealant pattern 110 is formed generates a stress greater than that in the active area 120. Moreover, since the UV-ray hardening sealant pattern 110 pulls the first and second substrates 100 and 150, the cell gap around the sealant pattern 110 may vary in accordance with the amount of the sealant pattern 110.
FIGS. 2A to 2G illustrate layouts and cross-sectional views illustrating a process of fabricating a liquid crystal display device using a related art liquid crystal dropping method.
A plurality of liquid crystal display panel regions are arranged on parent substrates (i.e., first and second substrates). As shown in FIG. 2A, a plurality of silver (Ag) patterns 201 are formed on the periphery of each liquid crystal display panel region on a first substrate 200.
Referring to FIG. 2B, column spacers 205 are formed in an active area of each liquid crystal display panel region on a second substrate 250 to correspond to a wiring part of the first substrate 200.
Referring to FIG. 2C, a UV-ray hardening sealant pattern 210 is formed on the periphery of each liquid crystal display panel region on the second substrate 250.
As shown in FIG. 2D, a predetermined amount of liquid crystal droplets 203 are dispensed on each liquid crystal display panel region of the first substrate 200. The second substrate 250 is disposed over the first substrate 200 to face into a bonding machine. The first and second substrates 200 and 250 are then bonded to each other. More specifically, the second substrate 250 is fixed to an upper stage 270 of the bonding machine, allowing movement in the Z-axis direction (i.e., vertical direction). Meanwhile, the silver (Ag) patterns 201 are disposed on the periphery of the UV-ray hardening sealant 210 on the second substrate 250. And, the first substrate 200 is fixed to a lower stage 260 of the bonding machine, allowing movement in the X and Y axes directions (i.e., horizontal direction).
Referring to FIG. 2E, the upper and lower stages 270 and 260 are aligned to each other, thereby achieving a vacuum condition within the bonding machine. Hence, the first and second substrates 200 and 250 are bonded to each other. After bonding the substrates 200 and 250 in the bonding machine under a vacuum condition, a first cell gap is formed, and then the bonded substrates 200 and 250 are exposed to the atmospheric pressure.
As shown in FIG. 2F, after the bonded substrates 200 and 250 having the first gap are exposed to the atmospheric pressure, a pressure difference between inside the liquid crystal display panel and the atmospheric pressure generates a second cell gap between the bonded substrates 200 and 250. In this case, the dispensed liquid crystal droplets become a liquid crystal layer 203a having a uniform thickness.
Referring to FIG. 2G, the bonded substrates 200 and 250 are placed on a quartz stage 280. A UV-ray is then irradiated to the bonded substrates on a lower side of the first substrate 200 in order to harden the UV-ray hardening sealant pattern 210.
The liquid crystal display device and the method of fabricating the same have the following problems or disadvantages.
The UV-ray hardening sealant pulls the bonded substrates while being hardened, thereby generating a stress between the active area part and the sealant pattern part. Since, the UV-ray hardening sealant pulls the bonded substrates while being hardened, the cell gap around the sealant pattern is altered in accordance with the quantity of the sealant pattern.